Method of making coated abrasives



March 24,1942. H. c. MARTIN ETAL 2,277,520

METHOD OF MAKING COATED ABRASIVES Filed March 2, 1936 INVENTORS HARRY C,MARTIN BY CARL. W. FOSS ATTdRNEY.

Patenterl Mar. 24, 1942 METHOD OF MAKING COATED ABRASIVES Harry 0.Martin and Carl W. Foss, Niagara Falls, N. Y., assignors, by mesneassignments, to The Carborundum Company, Niagara Falls, N. Y., acorporation of Delaware Application March 2, 1936, Serial No. 66,627

6 Claims.

This invention relates to an improved method of making coated abrasivearticles such as abrasive sheets, belts, discs, and the like.

One object of the invention is to provide an improved form of coatedabrasives characterized by an unusual cutting ability and exceptionallylong life. Another object of the invention is to provide a method formaking an article of the character described. Still another object ofthe invention is to provide abrasive articles and the method ofmanufacturing the same comprising a backing coat with a substantiallysingle layer of abrasive grains some of which are additionally coatedwith a second layer of grains whereby the coating will consist of areascovered by a substantially single layer of grains interspersed withclusters or mounds of additional grains attached to some of the firstmentioned grains.

Coated abrasive articles have heretofore commonly been made by coating abacking material with an adhesive, distributing the abrasive grain overthe surface of the adhesive, and then setting up the adhesive so as toattach the grains firmly to the backing. A second or sizing coating ofadhesive is commonly applied over the surface of the abrasive grains toassist in attaching them to the backing.

We have found that an abrasive coated product having a cutting rate andan abrading life upwards of 3 to 50% greater than the life of the usualarticles of this character can be made by first coating the backing witha restricted amount of grains and then adhesively coating the thuscoated articles with additional abrasive grains.

We have illustrated our invention by a number of drawings wherein:

Figure 1 is a side elevation of a backing coated with abrasive grainsand adhesive by the first step of our process;

Figure 2 represents the article of Figure 1 additionally coated with alayer of adhesive;

Figure 3 shows the article of Figure 2 additionally coated with a secondlayer of abrasive grains; and

Figure 4 illustrates one form of finished article made according to theinvention.

Referring to the drawing, Figure 1 shows a backing I to a surface ofwhich is attached abrasive grains 2 by an adhesive 3. In Figure 2, thearticle of Figure 1 has been additionally coated with a layer ofadhesive 4. In Figure 3, an adidtional coating of abrasive grains 5 hasbeen applied to the article of Figure 2 and in Figure 4 a final orsizing coating of adhesive 6 is shown applied to the article of Figure3.

In carrying out, the invention we commonly employ the conventionalmethods of applying the individual coats of adhesive and abrasivegrains. Such a method is fully described and illustrated in a bulletinissued by the Canadian Bureau of Mines as No. 699 entitled ArtificialAbrasives and Manufactured Abrasive Products and Their Uses (pp. 72 to79). Briefly, the method comprises passing a web between a pair ofrotating rolls, one of which is partially submerged in a vat of adhesivewhereby a layer of adhesive 3 is applied to the backing material I.

A controlled and restricted amount of grain is then applied uniformlyover the adhesive coated surface to form what is known in the art as anopen coating, the adhesive is hardened sufliciently to hold the grainsto the surface, and the thus coated web is passed between a second pair'of rotating rolls where the second making coat of adhesive 4 is appliedover the backing and over the tops of the grains 2. The thus coated webis then additionally coated with further abrasive grains 5 and isfinally sized with the adhesive coating 6 in the manner described inconnection with coatings 3 and 4. Following any or all of theapplications of adhesive the coated web may be suitably treated toharden the adhesive.

While it is customary to apply the adhesive and the abrasive grains inthe manner thus described, we sometimes find it convenient to apply oneor more of the coatings by other methods such as by spraying or bybrushing on the adhesive.

Furthermore, we have sometimes found it convenient to apply the thirdcoating about the abrasive granules before they are put on the backing.This application of adhesive may be put on by either mixing the abrasivegrains with a liquid adhesive or the grains may be covered with a layerof solid adhesive by any of a number of well known methods.

While most abrasive coated products are at present made with glue as theadhesive, our invention can be adapted to a variety of other adhesivessuch as resins, modified rubber, or other suitable adhesive material.These materials may be in the form of solutions, colloidal suspensionsor dispersions, or they may be normally liquid materials which are heathardenable such as certain phenolic condensation products whichare'liquid when first reacted but which are converted to a solidcondition by heating or other treatment,

The abrasive grains may be any of the types commonly employed such assilicon carbide, fused alumina, garnet or flint, and we have sometimesfound it useful to employ different kinds of grains for the twocoatings.

We have found that articles made in accordance with the method of ourinvention are exceptionally fast cutting and have unusually longabrading life, even with a weight of abrasive coating not materiallygreater than the weight of coating commonly employed by the oldermethods. Both the cutting rate and the abrading life are commonly foundto be from 30 to 50% greater than the rate and life of articles made bythe conventional method and carrying the same total weight of abrasivegrains per unit of area.

We usually apply from about to of the total weight of abrasive grain inthe first or open coating of grains 2 and the remainder in the secondcoating of grains 5. We have found that such proportions of the weightsof coatings are satisfactory.

Upon examination our articles appear to contain mounds or clusters ofgrains formed about the grains applied in the first coating,interspersed with areas carrying a single layer of grains which areattached directly to the backing. Apparently this particularconstruction of the abrasive coating provides clearance spaces for thestock removed by the grains when the articles are used. As stated, thearticles are very fast cutting and they are unusually sharp to thetouch. They feel like articles made with coarse grits but develop the.surface characteristic of the particular grit size employed.

While we have described and illustrated our invention with reference tocertain embodiments,

it is to'be understood that other modifications may be employed asdefined by the appended claims.

We claim:

1. In the method of making abrasive coated products the. steps whichcomprise coating a backing material with a layer of adhesive, applyingan open coating of abrasive grains to the ad hesive coating so as toleave a substantial proportion of the adhesive uncoated with the grains,and then additionally coating the coated surface with adhesive and. asecondary coating of abrasive grains, whereby the coated surfacecomprises uniformly distributed areas coated with single abrasive grainsinterspersed with areas coated with clusters containing a plurality ofgrains.

2. In the method of making abrasive coated products the steps whichcomprise first coating a backing with a substantially uniformlydistributed open coating of abrasive grains so as to leave a substantialproportion of the backing uncoated and then adhesively attaching asecond I an adhesive, applying a substantially uniformly I coating in anamount sufficient to substanti:.lly cover the previously uncoated partsof the backing and the grains which were first applied, whereby thecoated surface comprises uniformly distributed areas coated with singleabrasive grains interspersed with areas coated with clusters containinga plurality of grains.

3. In the method of making an abrasive article the steps which comprisecoating a backing material withan adhesive, applying a limited amount ofabrasive grain to the adhesive coating so as to coat only a minorproportion of the surface with grain substantially uniformly distributedas an open coating, applying a second coating of adhesive to the coatedside of the backing and then applying additional abrasive grain in aquantity sufficient to substantially completelycover both the adhesivesurface and the first coating of abrasive grains.

4. In the method of making an abrasive article the steps which comprisecoating a backing with distributed open coating of abrasive grains tothe backing in an amount sufficient to cover not more I than about 25per cent of the surface of the backing, applying a second coating ofadhesive to the thus coated backing, and then applying an additionalcoating of grains to the coated backing, whereby the coated surfacecomprises uniformly distributed areas coated with single abrasive grainsinterspersed with areas coated with clusters containing a plurality ofgrains.

5. In the method of making an abrasive article the steps which comprisecoating a backing material with an adhesive, applying a substantiallyuniformly distributed open coating of abrasive grain to the adhesivecoating so as to coat only a minor proportion of the surface with grain,applying a second coating of adhesive to the coated side of the backing,applying additional abrasive grain in. a quantity sufficient tosubstantially completely cover both the adhesive surface and the firstcoating of abrasive grains, and finally applying a third coating ofadhesive over the grain covered surfaces.

6. In the method of making an abrasive article the steps which comprisecoating a backing material with an adhesive, applying a substantiallyuniformly distributed open coating of abrasive grain to the adhesivecoating so as to coat only a minor proportion of the surface with grain,applying a second coating of adhesive to the coated side of the backingand then applying additional abrasive grains which have beenpreliminarily provided with coatings of solid adhesive, said additionalcoating'being made in a quantity sufficient to substantially completelycover both the adhesive surface and the first coating of abrasivegrains.

HARRY C. MARTIN. CARL W. FOSS.

